Daily News covers on mass shootings since Sandy Hook

The "Mysteries of Laura" star quickly deleted the tweet and checked herself in a series of contrite messages, explaining she had taken the gun-safety selfie as "part of a predetermined day of advocacy whose goal is to bring awareness to gun violence in America."

Thursday is National Gun Violence Awareness Day, a movement popularized by the nonprofit Everytown for Gun Safety that calls for people to wear orange in solidarity.

"AS I took the picture, the news broke about the shooting at UCLA. I was so shocked and struck by the horrible IRONY that yet another shooting was occurring as I was participating in this effort," she wrote. "In an effort to highlight the irony, I posted a picture referencing the breaking news."

Messing added that she was "heartbroken and embarrassed" that her well-intentioned tweet had been misinterpreted as an attention grab.

"The horrendous irony of the timing, I was hoping, would shine an even brighter light on the crisis and need for all of us to do something together to make the US safer," she wrote. "I am so truly sorry."

The victims in Wednesday's shooting, both men, were pronounced dead at the scene, Los Angeles police said. Officials declared the campus safe almost five hours after shots were fired.